I don't understand why? The ///M3 will still be the ///M3, it just offers a version for convertible fans, people who need 4 doors, and people who need the space (Touring). Why is this a bad thing?

Having the option of one doesn't make the other any "worse". It's not like BMW are forcing you to buy a Touring if you want a coupe If you don't like it, vote with your wallet, like Crimson said

All this does is it allows someone to buy a BMW performance car instead of a Audi Avant, Or a C63 station wagon. If there weren't alternatives, people would flock to where there is a suitable fit for their needs.

If BMW sell more cars, they have more money, and can continue to keep the ///M cars the benchmark. Audi are selling more and more cars, and Benz are a close contender, so if you want BMW to stay ahead, embrace what they are doing.